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1500 lines (1423 loc) · 44.7 KB
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/*
** 2013-03-14
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file contains code for a demonstration virtual table that finds
** "approximate matches" - strings from a finite set that are nearly the
** same as a single input string. The virtual table is called "amatch".
**
** A amatch virtual table is created like this:
**
** CREATE VIRTUAL TABLE f USING approximate_match(
** vocabulary_table=<tablename>, -- V
** vocabulary_word=<columnname>, -- W
** vocabulary_language=<columnname>, -- L
** edit_distances=<edit-cost-table>
** );
**
** When it is created, the new amatch table must be supplied with the
** the name of a table V and columns V.W and V.L such that
**
** SELECT W FROM V WHERE L=$language
**
** returns the allowed vocabulary for the match. If the "vocabulary_language"
** or L columnname is left unspecified or is an empty string, then no
** filtering of the vocabulary by language is performed.
**
** For efficiency, it is essential that the vocabulary table be indexed:
**
** CREATE vocab_index ON V(W)
**
** A separate edit-cost-table provides scoring information that defines
** what it means for one string to be "close" to another.
**
** The edit-cost-table must contain exactly four columns (more precisely,
** the statement "SELECT * FROM <edit-cost-table>" must return records
** that consist of four columns). It does not matter what the columns are
** named.
**
** Each row in the edit-cost-table represents a single character
** transformation going from user input to the vocabulary. The leftmost
** column of the row (column 0) contains an integer identifier of the
** language to which the transformation rule belongs (see "MULTIPLE LANGUAGES"
** below). The second column of the row (column 1) contains the input
** character or characters - the characters of user input. The third
** column contains characters as they appear in the vocabulary table.
** And the fourth column contains the integer cost of making the
** transformation. For example:
**
** CREATE TABLE f_data(iLang, cFrom, cTo, Cost);
** INSERT INTO f_data(iLang, cFrom, cTo, Cost) VALUES(0, '', 'a', 100);
** INSERT INTO f_data(iLang, cFrom, cTo, Cost) VALUES(0, 'b', '', 87);
** INSERT INTO f_data(iLang, cFrom, cTo, Cost) VALUES(0, 'o', 'oe', 38);
** INSERT INTO f_data(iLang, cFrom, cTo, Cost) VALUES(0, 'oe', 'o', 40);
**
** The first row inserted into the edit-cost-table by the SQL script
** above indicates that the cost of having an extra 'a' in the vocabulary
** table that is missing in the user input 100. (All costs are integers.
** Overall cost must not exceed 16777216.) The second INSERT statement
** creates a rule saying that the cost of having a single letter 'b' in
** user input which is missing in the vocabulary table is 87. The third
** INSERT statement mean that the cost of matching an 'o' in user input
** against an 'oe' in the vocabulary table is 38. And so forth.
**
** The following rules are special:
**
** INSERT INTO f_data(iLang, cFrom, cTo, Cost) VALUES(0, '?', '', 97);
** INSERT INTO f_data(iLang, cFrom, cTo, Cost) VALUES(0, '', '?', 98);
** INSERT INTO f_data(iLang, cFrom, cTo, Cost) VALUES(0, '?', '?', 99);
**
** The '?' to '' rule is the cost of having any single character in the input
** that is not found in the vocabular. The '' to '?' rule is the cost of
** having a character in the vocabulary table that is missing from input.
** And the '?' to '?' rule is the cost of doing an arbitrary character
** substitution. These three generic rules apply across all languages.
** In other words, the iLang field is ignored for the generic substitution
** rules. If more than one cost is given for a generic substitution rule,
** then the lowest cost is used.
**
** Once it has been created, the amatch virtual table can be queried
** as follows:
**
** SELECT word, distance FROM f
** WHERE word MATCH 'abcdefg'
** AND distance<200;
**
** This query outputs the strings contained in the T(F) field that
** are close to "abcdefg" and in order of increasing distance. No string
** is output more than once. If there are multiple ways to transform the
** target string ("abcdefg") into a string in the vocabulary table then
** the lowest cost transform is the one that is returned. In this example,
** the search is limited to strings with a total distance of less than 200.
**
** For efficiency, it is important to put tight bounds on the distance.
** The time and memory space needed to perform this query is exponential
** in the maximum distance. A good rule of thumb is to limit the distance
** to no more than 1.5 or 2 times the maximum cost of any rule in the
** edit-cost-table.
**
** The amatch is a read-only table. Any attempt to DELETE, INSERT, or
** UPDATE on a amatch table will throw an error.
**
** It is important to put some kind of a limit on the amatch output. This
** can be either in the form of a LIMIT clause at the end of the query,
** or better, a "distance<NNN" constraint where NNN is some number. The
** running time and memory requirement is exponential in the value of NNN
** so you want to make sure that NNN is not too big. A value of NNN that
** is about twice the average transformation cost seems to give good results.
**
** The amatch table can be useful for tasks such as spelling correction.
** Suppose all allowed words are in table vocabulary(w). Then one would create
** an amatch virtual table like this:
**
** CREATE VIRTUAL TABLE ex1 USING amatch(
** vocabtable=vocabulary,
** vocabcolumn=w,
** edit_distances=ec1
** );
**
** Then given an input word $word, look up close spellings this way:
**
** SELECT word, distance FROM ex1
** WHERE word MATCH $word AND distance<200;
**
** MULTIPLE LANGUAGES
**
** Normally, the "iLang" value associated with all character transformations
** in the edit-cost-table is zero. However, if required, the amatch
** virtual table allows multiple languages to be defined. Each query uses
** only a single iLang value. This allows, for example, a single
** amatch table to support multiple languages.
**
** By default, only the rules with iLang=0 are used. To specify an
** alternative language, a "language = ?" expression must be added to the
** WHERE clause of a SELECT, where ? is the integer identifier of the desired
** language. For example:
**
** SELECT word, distance FROM ex1
** WHERE word MATCH $word
** AND distance<=200
** AND language=1 -- Specify use language 1 instead of 0
**
** If no "language = ?" constraint is specified in the WHERE clause, language
** 0 is used.
**
** LIMITS
**
** The maximum language number is 2147483647. The maximum length of either
** of the strings in the second or third column of the amatch data table
** is 50 bytes. The maximum cost on a rule is 1000.
*/
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <stdio.h>
#include <ctype.h>
#ifndef SQLITE_OMIT_VIRTUALTABLE
/*
** Forward declaration of objects used by this implementation
*/
typedef struct amatch_vtab amatch_vtab;
typedef struct amatch_cursor amatch_cursor;
typedef struct amatch_rule amatch_rule;
typedef struct amatch_word amatch_word;
typedef struct amatch_avl amatch_avl;
/*****************************************************************************
** AVL Tree implementation
*/
/*
** Objects that want to be members of the AVL tree should embedded an
** instance of this structure.
*/
struct amatch_avl {
amatch_word *pWord; /* Points to the object being stored in the tree */
char *zKey; /* Key. zero-terminated string. Must be unique */
amatch_avl *pBefore; /* Other elements less than zKey */
amatch_avl *pAfter; /* Other elements greater than zKey */
amatch_avl *pUp; /* Parent element */
short int height; /* Height of this node. Leaf==1 */
short int imbalance; /* Height difference between pBefore and pAfter */
};
/* Recompute the amatch_avl.height and amatch_avl.imbalance fields for p.
** Assume that the children of p have correct heights.
*/
static void amatchAvlRecomputeHeight(amatch_avl *p){
short int hBefore = p->pBefore ? p->pBefore->height : 0;
short int hAfter = p->pAfter ? p->pAfter->height : 0;
p->imbalance = hBefore - hAfter; /* -: pAfter higher. +: pBefore higher */
p->height = (hBefore>hAfter ? hBefore : hAfter)+1;
}
/*
** P B
** / \ / \
** B Z ==> X P
** / \ / \
** X Y Y Z
**
*/
static amatch_avl *amatchAvlRotateBefore(amatch_avl *pP){
amatch_avl *pB = pP->pBefore;
amatch_avl *pY = pB->pAfter;
pB->pUp = pP->pUp;
pB->pAfter = pP;
pP->pUp = pB;
pP->pBefore = pY;
if( pY ) pY->pUp = pP;
amatchAvlRecomputeHeight(pP);
amatchAvlRecomputeHeight(pB);
return pB;
}
/*
** P A
** / \ / \
** X A ==> P Z
** / \ / \
** Y Z X Y
**
*/
static amatch_avl *amatchAvlRotateAfter(amatch_avl *pP){
amatch_avl *pA = pP->pAfter;
amatch_avl *pY = pA->pBefore;
pA->pUp = pP->pUp;
pA->pBefore = pP;
pP->pUp = pA;
pP->pAfter = pY;
if( pY ) pY->pUp = pP;
amatchAvlRecomputeHeight(pP);
amatchAvlRecomputeHeight(pA);
return pA;
}
/*
** Return a pointer to the pBefore or pAfter pointer in the parent
** of p that points to p. Or if p is the root node, return pp.
*/
static amatch_avl **amatchAvlFromPtr(amatch_avl *p, amatch_avl **pp){
amatch_avl *pUp = p->pUp;
if( pUp==0 ) return pp;
if( pUp->pAfter==p ) return &pUp->pAfter;
return &pUp->pBefore;
}
/*
** Rebalance all nodes starting with p and working up to the root.
** Return the new root.
*/
static amatch_avl *amatchAvlBalance(amatch_avl *p){
amatch_avl *pTop = p;
amatch_avl **pp;
while( p ){
amatchAvlRecomputeHeight(p);
if( p->imbalance>=2 ){
amatch_avl *pB = p->pBefore;
if( pB->imbalance<0 ) p->pBefore = amatchAvlRotateAfter(pB);
pp = amatchAvlFromPtr(p,&p);
p = *pp = amatchAvlRotateBefore(p);
}else if( p->imbalance<=(-2) ){
amatch_avl *pA = p->pAfter;
if( pA->imbalance>0 ) p->pAfter = amatchAvlRotateBefore(pA);
pp = amatchAvlFromPtr(p,&p);
p = *pp = amatchAvlRotateAfter(p);
}
pTop = p;
p = p->pUp;
}
return pTop;
}
/* Search the tree rooted at p for an entry with zKey. Return a pointer
** to the entry or return NULL.
*/
static amatch_avl *amatchAvlSearch(amatch_avl *p, const char *zKey){
int c;
while( p && (c = strcmp(zKey, p->zKey))!=0 ){
p = (c<0) ? p->pBefore : p->pAfter;
}
return p;
}
/* Find the first node (the one with the smallest key).
*/
static amatch_avl *amatchAvlFirst(amatch_avl *p){
if( p ) while( p->pBefore ) p = p->pBefore;
return p;
}
#if 0 /* NOT USED */
/* Return the node with the next larger key after p.
*/
static amatch_avl *amatchAvlNext(amatch_avl *p){
amatch_avl *pPrev = 0;
while( p && p->pAfter==pPrev ){
pPrev = p;
p = p->pUp;
}
if( p && pPrev==0 ){
p = amatchAvlFirst(p->pAfter);
}
return p;
}
#endif
#if 0 /* NOT USED */
/* Verify AVL tree integrity
*/
static int amatchAvlIntegrity(amatch_avl *pHead){
amatch_avl *p;
if( pHead==0 ) return 1;
if( (p = pHead->pBefore)!=0 ){
assert( p->pUp==pHead );
assert( amatchAvlIntegrity(p) );
assert( strcmp(p->zKey, pHead->zKey)<0 );
while( p->pAfter ) p = p->pAfter;
assert( strcmp(p->zKey, pHead->zKey)<0 );
}
if( (p = pHead->pAfter)!=0 ){
assert( p->pUp==pHead );
assert( amatchAvlIntegrity(p) );
assert( strcmp(p->zKey, pHead->zKey)>0 );
p = amatchAvlFirst(p);
assert( strcmp(p->zKey, pHead->zKey)>0 );
}
return 1;
}
static int amatchAvlIntegrity2(amatch_avl *pHead){
amatch_avl *p, *pNext;
for(p=amatchAvlFirst(pHead); p; p=pNext){
pNext = amatchAvlNext(p);
if( pNext==0 ) break;
assert( strcmp(p->zKey, pNext->zKey)<0 );
}
return 1;
}
#endif
/* Insert a new node pNew. Return NULL on success. If the key is not
** unique, then do not perform the insert but instead leave pNew unchanged
** and return a pointer to an existing node with the same key.
*/
static amatch_avl *amatchAvlInsert(amatch_avl **ppHead, amatch_avl *pNew){
int c;
amatch_avl *p = *ppHead;
if( p==0 ){
p = pNew;
pNew->pUp = 0;
}else{
while( p ){
c = strcmp(pNew->zKey, p->zKey);
if( c<0 ){
if( p->pBefore ){
p = p->pBefore;
}else{
p->pBefore = pNew;
pNew->pUp = p;
break;
}
}else if( c>0 ){
if( p->pAfter ){
p = p->pAfter;
}else{
p->pAfter = pNew;
pNew->pUp = p;
break;
}
}else{
return p;
}
}
}
pNew->pBefore = 0;
pNew->pAfter = 0;
pNew->height = 1;
pNew->imbalance = 0;
*ppHead = amatchAvlBalance(p);
/* assert( amatchAvlIntegrity(*ppHead) ); */
/* assert( amatchAvlIntegrity2(*ppHead) ); */
return 0;
}
/* Remove node pOld from the tree. pOld must be an element of the tree or
** the AVL tree will become corrupt.
*/
static void amatchAvlRemove(amatch_avl **ppHead, amatch_avl *pOld){
amatch_avl **ppParent;
amatch_avl *pBalance = 0;
/* assert( amatchAvlSearch(*ppHead, pOld->zKey)==pOld ); */
ppParent = amatchAvlFromPtr(pOld, ppHead);
if( pOld->pBefore==0 && pOld->pAfter==0 ){
*ppParent = 0;
pBalance = pOld->pUp;
}else if( pOld->pBefore && pOld->pAfter ){
amatch_avl *pX, *pY;
pX = amatchAvlFirst(pOld->pAfter);
*amatchAvlFromPtr(pX, 0) = pX->pAfter;
if( pX->pAfter ) pX->pAfter->pUp = pX->pUp;
pBalance = pX->pUp;
pX->pAfter = pOld->pAfter;
if( pX->pAfter ){
pX->pAfter->pUp = pX;
}else{
assert( pBalance==pOld );
pBalance = pX;
}
pX->pBefore = pY = pOld->pBefore;
if( pY ) pY->pUp = pX;
pX->pUp = pOld->pUp;
*ppParent = pX;
}else if( pOld->pBefore==0 ){
*ppParent = pBalance = pOld->pAfter;
pBalance->pUp = pOld->pUp;
}else if( pOld->pAfter==0 ){
*ppParent = pBalance = pOld->pBefore;
pBalance->pUp = pOld->pUp;
}
*ppHead = amatchAvlBalance(pBalance);
pOld->pUp = 0;
pOld->pBefore = 0;
pOld->pAfter = 0;
/* assert( amatchAvlIntegrity(*ppHead) ); */
/* assert( amatchAvlIntegrity2(*ppHead) ); */
}
/*
** End of the AVL Tree implementation
******************************************************************************/
/*
** Various types.
**
** amatch_cost is the "cost" of an edit operation.
**
** amatch_len is the length of a matching string.
**
** amatch_langid is an ruleset identifier.
*/
typedef int amatch_cost;
typedef signed char amatch_len;
typedef int amatch_langid;
/*
** Limits
*/
#define AMATCH_MX_LENGTH 50 /* Maximum length of a rule string */
#define AMATCH_MX_LANGID 2147483647 /* Maximum rule ID */
#define AMATCH_MX_COST 1000 /* Maximum single-rule cost */
/*
** A match or partial match
*/
struct amatch_word {
amatch_word *pNext; /* Next on a list of all amatch_words */
amatch_avl sCost; /* Linkage of this node into the cost tree */
amatch_avl sWord; /* Linkage of this node into the word tree */
amatch_cost rCost; /* Cost of the match so far */
int iSeq; /* Sequence number */
char zCost[10]; /* Cost key (text rendering of rCost) */
short int nMatch; /* Input characters matched */
char zWord[4]; /* Text of the word. Extra space appended as needed */
};
/*
** Each transformation rule is stored as an instance of this object.
** All rules are kept on a linked list sorted by rCost.
*/
struct amatch_rule {
amatch_rule *pNext; /* Next rule in order of increasing rCost */
char *zFrom; /* Transform from (a string from user input) */
amatch_cost rCost; /* Cost of this transformation */
amatch_langid iLang; /* The langauge to which this rule belongs */
amatch_len nFrom, nTo; /* Length of the zFrom and zTo strings */
char zTo[4]; /* Tranform to V.W value (extra space appended) */
};
/*
** A amatch virtual-table object
*/
struct amatch_vtab {
sqlite3_vtab base; /* Base class - must be first */
char *zClassName; /* Name of this class. Default: "amatch" */
char *zDb; /* Name of database. (ex: "main") */
char *zSelf; /* Name of this virtual table */
char *zCostTab; /* Name of edit-cost-table */
char *zVocabTab; /* Name of vocabulary table */
char *zVocabWord; /* Name of vocabulary table word column */
char *zVocabLang; /* Name of vocabulary table language column */
amatch_rule *pRule; /* All active rules in this amatch */
amatch_cost rIns; /* Generic insertion cost '' -> ? */
amatch_cost rDel; /* Generic deletion cost ? -> '' */
amatch_cost rSub; /* Generic substitution cost ? -> ? */
sqlite3 *db; /* The database connection */
sqlite3_stmt *pVCheck; /* Query to check zVocabTab */
int nCursor; /* Number of active cursors */
};
/* A amatch cursor object */
struct amatch_cursor {
sqlite3_vtab_cursor base; /* Base class - must be first */
sqlite3_int64 iRowid; /* The rowid of the current word */
amatch_langid iLang; /* Use this language ID */
amatch_cost rLimit; /* Maximum cost of any term */
int nBuf; /* Space allocated for zBuf */
int oomErr; /* True following an OOM error */
int nWord; /* Number of amatch_word objects */
char *zBuf; /* Temp-use buffer space */
char *zInput; /* Input word to match against */
amatch_vtab *pVtab; /* The virtual table this cursor belongs to */
amatch_word *pAllWords; /* List of all amatch_word objects */
amatch_word *pCurrent; /* Most recent solution */
amatch_avl *pCost; /* amatch_word objects keyed by iCost */
amatch_avl *pWord; /* amatch_word objects keyed by zWord */
};
/*
** The two input rule lists are both sorted in order of increasing
** cost. Merge them together into a single list, sorted by cost, and
** return a pointer to the head of that list.
*/
static amatch_rule *amatchMergeRules(amatch_rule *pA, amatch_rule *pB){
amatch_rule head;
amatch_rule *pTail;
pTail = &head;
while( pA && pB ){
if( pA->rCost<=pB->rCost ){
pTail->pNext = pA;
pTail = pA;
pA = pA->pNext;
}else{
pTail->pNext = pB;
pTail = pB;
pB = pB->pNext;
}
}
if( pA==0 ){
pTail->pNext = pB;
}else{
pTail->pNext = pA;
}
return head.pNext;
}
/*
** Statement pStmt currently points to a row in the amatch data table. This
** function allocates and populates a amatch_rule structure according to
** the content of the row.
**
** If successful, *ppRule is set to point to the new object and SQLITE_OK
** is returned. Otherwise, *ppRule is zeroed, *pzErr may be set to point
** to an error message and an SQLite error code returned.
*/
static int amatchLoadOneRule(
amatch_vtab *p, /* Fuzzer virtual table handle */
sqlite3_stmt *pStmt, /* Base rule on statements current row */
amatch_rule **ppRule, /* OUT: New rule object */
char **pzErr /* OUT: Error message */
){
sqlite3_int64 iLang = sqlite3_column_int64(pStmt, 0);
const char *zFrom = (const char *)sqlite3_column_text(pStmt, 1);
const char *zTo = (const char *)sqlite3_column_text(pStmt, 2);
amatch_cost rCost = sqlite3_column_int(pStmt, 3);
int rc = SQLITE_OK; /* Return code */
int nFrom; /* Size of string zFrom, in bytes */
int nTo; /* Size of string zTo, in bytes */
amatch_rule *pRule = 0; /* New rule object to return */
if( zFrom==0 ) zFrom = "";
if( zTo==0 ) zTo = "";
nFrom = (int)strlen(zFrom);
nTo = (int)strlen(zTo);
/* Silently ignore null transformations */
if( strcmp(zFrom, zTo)==0 ){
if( zFrom[0]=='?' && zFrom[1]==0 ){
if( p->rSub==0 || p->rSub>rCost ) p->rSub = rCost;
}
*ppRule = 0;
return SQLITE_OK;
}
if( rCost<=0 || rCost>AMATCH_MX_COST ){
*pzErr = sqlite3_mprintf("%s: cost must be between 1 and %d",
p->zClassName, AMATCH_MX_COST
);
rc = SQLITE_ERROR;
}else
if( nFrom>AMATCH_MX_LENGTH || nTo>AMATCH_MX_LENGTH ){
*pzErr = sqlite3_mprintf("%s: maximum string length is %d",
p->zClassName, AMATCH_MX_LENGTH
);
rc = SQLITE_ERROR;
}else
if( iLang<0 || iLang>AMATCH_MX_LANGID ){
*pzErr = sqlite3_mprintf("%s: iLang must be between 0 and %d",
p->zClassName, AMATCH_MX_LANGID
);
rc = SQLITE_ERROR;
}else
if( strcmp(zFrom,"")==0 && strcmp(zTo,"?")==0 ){
if( p->rIns==0 || p->rIns>rCost ) p->rIns = rCost;
}else
if( strcmp(zFrom,"?")==0 && strcmp(zTo,"")==0 ){
if( p->rDel==0 || p->rDel>rCost ) p->rDel = rCost;
}else
{
pRule = sqlite3_malloc( sizeof(*pRule) + nFrom + nTo );
if( pRule==0 ){
rc = SQLITE_NOMEM;
}else{
memset(pRule, 0, sizeof(*pRule));
pRule->zFrom = &pRule->zTo[nTo+1];
pRule->nFrom = (amatch_len)nFrom;
memcpy(pRule->zFrom, zFrom, nFrom+1);
memcpy(pRule->zTo, zTo, nTo+1);
pRule->nTo = (amatch_len)nTo;
pRule->rCost = rCost;
pRule->iLang = (int)iLang;
}
}
*ppRule = pRule;
return rc;
}
/*
** Free all the content in the edit-cost-table
*/
static void amatchFreeRules(amatch_vtab *p){
while( p->pRule ){
amatch_rule *pRule = p->pRule;
p->pRule = pRule->pNext;
sqlite3_free(pRule);
}
p->pRule = 0;
}
/*
** Load the content of the amatch data table into memory.
*/
static int amatchLoadRules(
sqlite3 *db, /* Database handle */
amatch_vtab *p, /* Virtual amatch table to configure */
char **pzErr /* OUT: Error message */
){
int rc = SQLITE_OK; /* Return code */
char *zSql; /* SELECT used to read from rules table */
amatch_rule *pHead = 0;
zSql = sqlite3_mprintf("SELECT * FROM %Q.%Q", p->zDb, p->zCostTab);
if( zSql==0 ){
rc = SQLITE_NOMEM;
}else{
int rc2; /* finalize() return code */
sqlite3_stmt *pStmt = 0;
rc = sqlite3_prepare_v2(db, zSql, -1, &pStmt, 0);
if( rc!=SQLITE_OK ){
*pzErr = sqlite3_mprintf("%s: %s", p->zClassName, sqlite3_errmsg(db));
}else if( sqlite3_column_count(pStmt)!=4 ){
*pzErr = sqlite3_mprintf("%s: %s has %d columns, expected 4",
p->zClassName, p->zCostTab, sqlite3_column_count(pStmt)
);
rc = SQLITE_ERROR;
}else{
while( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
amatch_rule *pRule = 0;
rc = amatchLoadOneRule(p, pStmt, &pRule, pzErr);
if( pRule ){
pRule->pNext = pHead;
pHead = pRule;
}
}
}
rc2 = sqlite3_finalize(pStmt);
if( rc==SQLITE_OK ) rc = rc2;
}
sqlite3_free(zSql);
/* All rules are now in a singly linked list starting at pHead. This
** block sorts them by cost and then sets amatch_vtab.pRule to point to
** point to the head of the sorted list.
*/
if( rc==SQLITE_OK ){
unsigned int i;
amatch_rule *pX;
amatch_rule *a[15];
for(i=0; i<sizeof(a)/sizeof(a[0]); i++) a[i] = 0;
while( (pX = pHead)!=0 ){
pHead = pX->pNext;
pX->pNext = 0;
for(i=0; a[i] && i<sizeof(a)/sizeof(a[0])-1; i++){
pX = amatchMergeRules(a[i], pX);
a[i] = 0;
}
a[i] = amatchMergeRules(a[i], pX);
}
for(pX=a[0], i=1; i<sizeof(a)/sizeof(a[0]); i++){
pX = amatchMergeRules(a[i], pX);
}
p->pRule = amatchMergeRules(p->pRule, pX);
}else{
/* An error has occurred. Setting p->pRule to point to the head of the
** allocated list ensures that the list will be cleaned up in this case.
*/
assert( p->pRule==0 );
p->pRule = pHead;
}
return rc;
}
/*
** This function converts an SQL quoted string into an unquoted string
** and returns a pointer to a buffer allocated using sqlite3_malloc()
** containing the result. The caller should eventually free this buffer
** using sqlite3_free.
**
** Examples:
**
** "abc" becomes abc
** 'xyz' becomes xyz
** [pqr] becomes pqr
** `mno` becomes mno
*/
static char *amatchDequote(const char *zIn){
int nIn; /* Size of input string, in bytes */
char *zOut; /* Output (dequoted) string */
nIn = (int)strlen(zIn);
zOut = sqlite3_malloc(nIn+1);
if( zOut ){
char q = zIn[0]; /* Quote character (if any ) */
if( q!='[' && q!= '\'' && q!='"' && q!='`' ){
memcpy(zOut, zIn, nIn+1);
}else{
int iOut = 0; /* Index of next byte to write to output */
int iIn; /* Index of next byte to read from input */
if( q=='[' ) q = ']';
for(iIn=1; iIn<nIn; iIn++){
if( zIn[iIn]==q ) iIn++;
zOut[iOut++] = zIn[iIn];
}
}
assert( (int)strlen(zOut)<=nIn );
}
return zOut;
}
/*
** Deallocate the pVCheck prepared statement.
*/
static void amatchVCheckClear(amatch_vtab *p){
if( p->pVCheck ){
sqlite3_finalize(p->pVCheck);
p->pVCheck = 0;
}
}
/*
** Deallocate an amatch_vtab object
*/
static void amatchFree(amatch_vtab *p){
if( p ){
amatchFreeRules(p);
amatchVCheckClear(p);
sqlite3_free(p->zClassName);
sqlite3_free(p->zDb);
sqlite3_free(p->zCostTab);
sqlite3_free(p->zVocabTab);
sqlite3_free(p->zVocabWord);
sqlite3_free(p->zVocabLang);
sqlite3_free(p->zSelf);
memset(p, 0, sizeof(*p));
sqlite3_free(p);
}
}
/*
** xDisconnect/xDestroy method for the amatch module.
*/
static int amatchDisconnect(sqlite3_vtab *pVtab){
amatch_vtab *p = (amatch_vtab*)pVtab;
assert( p->nCursor==0 );
amatchFree(p);
return SQLITE_OK;
}
/*
** Check to see if the argument is of the form:
**
** KEY = VALUE
**
** If it is, return a pointer to the first character of VALUE.
** If not, return NULL. Spaces around the = are ignored.
*/
static const char *amatchValueOfKey(const char *zKey, const char *zStr){
int nKey = (int)strlen(zKey);
int nStr = (int)strlen(zStr);
int i;
if( nStr<nKey+1 ) return 0;
if( memcmp(zStr, zKey, nKey)!=0 ) return 0;
for(i=nKey; isspace((unsigned char)zStr[i]); i++){}
if( zStr[i]!='=' ) return 0;
i++;
while( isspace((unsigned char)zStr[i]) ){ i++; }
return zStr+i;
}
/*
** xConnect/xCreate method for the amatch module. Arguments are:
**
** argv[0] -> module name ("approximate_match")
** argv[1] -> database name
** argv[2] -> table name
** argv[3...] -> arguments
*/
static int amatchConnect(
sqlite3 *db,
void *pAux,
int argc, const char *const*argv,
sqlite3_vtab **ppVtab,
char **pzErr
){
int rc = SQLITE_OK; /* Return code */
amatch_vtab *pNew = 0; /* New virtual table */
const char *zModule = argv[0];
const char *zDb = argv[1];
const char *zVal;
int i;
(void)pAux;
*ppVtab = 0;
pNew = sqlite3_malloc( sizeof(*pNew) );
if( pNew==0 ) return SQLITE_NOMEM;
rc = SQLITE_NOMEM;
memset(pNew, 0, sizeof(*pNew));
pNew->db = db;
pNew->zClassName = sqlite3_mprintf("%s", zModule);
if( pNew->zClassName==0 ) goto amatchConnectError;
pNew->zDb = sqlite3_mprintf("%s", zDb);
if( pNew->zDb==0 ) goto amatchConnectError;
pNew->zSelf = sqlite3_mprintf("%s", argv[2]);
if( pNew->zSelf==0 ) goto amatchConnectError;
for(i=3; i<argc; i++){
zVal = amatchValueOfKey("vocabulary_table", argv[i]);
if( zVal ){
sqlite3_free(pNew->zVocabTab);
pNew->zVocabTab = amatchDequote(zVal);
if( pNew->zVocabTab==0 ) goto amatchConnectError;
continue;
}
zVal = amatchValueOfKey("vocabulary_word", argv[i]);
if( zVal ){
sqlite3_free(pNew->zVocabWord);
pNew->zVocabWord = amatchDequote(zVal);
if( pNew->zVocabWord==0 ) goto amatchConnectError;
continue;
}
zVal = amatchValueOfKey("vocabulary_language", argv[i]);
if( zVal ){
sqlite3_free(pNew->zVocabLang);
pNew->zVocabLang = amatchDequote(zVal);
if( pNew->zVocabLang==0 ) goto amatchConnectError;
continue;
}
zVal = amatchValueOfKey("edit_distances", argv[i]);
if( zVal ){
sqlite3_free(pNew->zCostTab);
pNew->zCostTab = amatchDequote(zVal);
if( pNew->zCostTab==0 ) goto amatchConnectError;
continue;
}
*pzErr = sqlite3_mprintf("unrecognized argument: [%s]\n", argv[i]);
amatchFree(pNew);
*ppVtab = 0;
return SQLITE_ERROR;
}
rc = SQLITE_OK;
if( pNew->zCostTab==0 ){
*pzErr = sqlite3_mprintf("no edit_distances table specified");
rc = SQLITE_ERROR;
}else{
rc = amatchLoadRules(db, pNew, pzErr);
}
if( rc==SQLITE_OK ){
rc = sqlite3_declare_vtab(db,
"CREATE TABLE x(word,distance,language,"
"command HIDDEN,nword HIDDEN)"
);
#define AMATCH_COL_WORD 0
#define AMATCH_COL_DISTANCE 1
#define AMATCH_COL_LANGUAGE 2
#define AMATCH_COL_COMMAND 3
#define AMATCH_COL_NWORD 4
}
if( rc!=SQLITE_OK ){
amatchFree(pNew);
}
*ppVtab = &pNew->base;
return rc;
amatchConnectError:
amatchFree(pNew);
return rc;
}
/*
** Open a new amatch cursor.
*/
static int amatchOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
amatch_vtab *p = (amatch_vtab*)pVTab;
amatch_cursor *pCur;
pCur = sqlite3_malloc( sizeof(*pCur) );
if( pCur==0 ) return SQLITE_NOMEM;
memset(pCur, 0, sizeof(*pCur));
pCur->pVtab = p;
*ppCursor = &pCur->base;
p->nCursor++;
return SQLITE_OK;
}
/*
** Free up all the memory allocated by a cursor. Set it rLimit to 0
** to indicate that it is at EOF.
*/
static void amatchClearCursor(amatch_cursor *pCur){
amatch_word *pWord, *pNextWord;
for(pWord=pCur->pAllWords; pWord; pWord=pNextWord){
pNextWord = pWord->pNext;
sqlite3_free(pWord);
}
pCur->pAllWords = 0;
sqlite3_free(pCur->zInput);
pCur->zInput = 0;
sqlite3_free(pCur->zBuf);
pCur->zBuf = 0;
pCur->nBuf = 0;
pCur->pCost = 0;
pCur->pWord = 0;
pCur->pCurrent = 0;
pCur->rLimit = 1000000;
pCur->iLang = 0;
pCur->nWord = 0;
}
/*
** Close a amatch cursor.
*/
static int amatchClose(sqlite3_vtab_cursor *cur){
amatch_cursor *pCur = (amatch_cursor *)cur;
amatchClearCursor(pCur);
pCur->pVtab->nCursor--;
sqlite3_free(pCur);
return SQLITE_OK;
}
/*
** Render a 24-bit unsigned integer as a 4-byte base-64 number.
*/
static void amatchEncodeInt(int x, char *z){
static const char a[] =
"0123456789"
"ABCDEFGHIJ"
"KLMNOPQRST"
"UVWXYZ^abc"
"defghijklm"
"nopqrstuvw"
"xyz~";
z[0] = a[(x>>18)&0x3f];
z[1] = a[(x>>12)&0x3f];
z[2] = a[(x>>6)&0x3f];
z[3] = a[x&0x3f];
}
/*
** Write the zCost[] field for a amatch_word object
*/
static void amatchWriteCost(amatch_word *pWord){
amatchEncodeInt(pWord->rCost, pWord->zCost);
amatchEncodeInt(pWord->iSeq, pWord->zCost+4);
pWord->zCost[8] = 0;
}